TAYLOR and NAISH – A FREAKY WEALDEN BRACHIOSAUR of
A freaky Wealden brachiosaur (Dinosauria; Sauropoda) THAT EVERYONE SHOULD JOLLY WELL SIT UP STRAIGHT AND PAY ATTENTION TO
by MICHAEL P. TAYLOR and DARREN NAISH
School of Earth and Environmental Sciences, University of Portsmouth, Portsmouth PO1 3QL, UK.
e-mail: email@example.com and firstname.lastname@example.org Key words: Dinosauria, Sauropoda, Brachiosauridae, Wealden, Cretaceous
Please note contact details for correspondence and proofs:
Mike Taylor, Oakleigh Farm House, Crooked End, Ruardean GL17 9XF, ENGLAND
Tel. +44 1594 546 941; Fax. +44 1594 546 942
### to follow
The remains of sauropod dinosaurs have been known from the Lower Cretaceous Wealden rocks of the English mainland since the 1840s. Though it should be noted that sauropods were not recognised as a distinct dinosaurian group until somewhat later ([Phillips1871], [Marsh1878]), the first named sauropod, Cetiosaurus brevis Owen 1841/2, was coined for Wealden material (Naish and Martill (2001), Upchurch and Martin (2003)).
Most Wealden sauropods are from the Barremian Wessex Formation of the Isle of Wight. With the exception of the as-yet-undescribed Barnes High partial skeleton, all Wessex Formation sauropods are based on highly incomplete remains. Even so, it is possible to determine the presence of at least three higher-level taxa. An indeterminate, unnamed diplodocoid is represented by teeth and fragmentary postcranial elements (Naish and Martill (2001)). Members of Brachiosauridae are certainly present in the Wessex Formation as isolated cervical and dorsal vertebrae, and the Barnes High partial skeleton, share derived characters with the Upper Jurassic taxon Brachiosaurus (Blows (1995), Upchurch (1995), Naish and Martill (2001), Naish et al. (2004)). Finally, indeterminate members of Titanosauria, represented by caudal vertebrae known by the nomen dubiumIuticosaurus valdensis (Huene (1929)), are also present. A large, unusual tooth (the holotype of Oplosaurus armatus Gervais 1852) appears not to belong to any of these groups and may represent a fourth group. While eight species-level names are attached to these remains, it remains impossible to determine which are synonymous given that they are mostly named on non-overlapping holotypes. Furthermore, with the problematic exceptions of Eucamerotus foxi Blows 1995 and Oplosaurus armatus, none are attached to diagnostic specimens. While taxonomic problems do exist, it is not correct to imply that Wessex Formation sauropods require revision, given that taxonomic appraisals of the eight species-level names have recently been provided (Blows (1995), Naish and Martill (2001), Wilson and Upchurch. (2003)). However, the confusing and probably over-split taxonomy of Wessex Formation sauropods cannot be resolved until additional, diagnostic material is described or discovered.
Far less well represented than the Wessex Formation sauropods are those of the older Berriasian-Valanginian ([AllenWimbledon1991]) Hastings Beds Group of the mainland Wealden. The specimens have been collected from Cuckfield (West Sussex), Hastings (East Sussex) and most recently from Bexhill (East Sussex) and, intriguingly, there are indications that a taxonomic diversity similar to that of the Wessex Formation is present among these forms. Cetiosaurus brevis (including Pelorosaurus conybeari – see discussion), though conventionally interpreted as a brachiosaurid (McIntosh (1990), Naish and Martill (2001)), was argued to be an indeterminate basal titanosauriform by Upchurch et al. (2004)). Pelorosaurus becklesii Mantell 1852 consists of a partial humerus, radius and ulna, and associated skin impressions, and, on the basis of the robustness of its forelimb elements, appears to be a titanosaur (Upchurch (1995), Upchurch et al. (2004)). Finally, an isolated metacarpal from Bexhill Beach, derived from the Hastings Beds Group, has been identified as diplodocoid ([Anon2005]).
Here we redescribe a Hastings Beds Group specimen first reported, briefly, by Lydekker (1893). Though consisting only of a single incomplete vertebra, it preserves a large number of phylogenetically informative characters that allow it to be identified with confidence. Furthermore, it is highly distinctive, possessing other characters that can be regarded as autapomorphies. While it is tempting to be highly critical of attempts to assess the validity of sauropod taxa known only from isolated vertebrae, it should be emphasised that sauropod vertebrae are highly diagnostic and recognisable at the specific level [### maybe cite some refs showing this – perhaps any that distinguish sauropods on vertebral characters alone?]. The addition of what may be another sauropod taxon to the Hastings Beds Group should also not be regarded as problematical given that we now know of many Mesozoic faunas and geological horizons where several sauropod species and genera were contemporaneous.
[### This intro was obviously written as a ‘We’re going to look at a Wealden specimen, so let’s start off by reminding you about Wealden sauropods’ piece. Are you ok with this, or were you thinking more along the lines of ‘We’re going to look at a sauropod vertebra, so let’s start off by reminding you about sauropod vertebrae’?]
Anatomical abbreviations: ACPL, anterior centroparapophyseal lamina; CPRL, centroprezygapophyseal lamina; PCPL, posterior centroparapophyseal lamina; PODL, postzygadiapophyseal lamina; PRPL, prezygaparapophyseal lamina; PPDL, paradiapophyseal lamina. We follow the vertebral lamina nomenclature of Wilson (1999) except in using capital letters for the abbreviations, a convention that allows plurals to be more clearly formed.
Institutional abbreviations: BMNH, British Museum (Natural History), London, England; HMN, Humboldt Museum fur Naturkunde, Berlin, Germany.
Etymology – ### genus to follow; ruffordi after Philip James Rufford, the discoverer of the material.
Holotype – BMNH R2095, posterior dorsal vertebra consisting of partial centrum and neural arch.
Locality and Horizon – Fairlight, Hastings Beds Group. Three miles east of Hastings, East Sussex, United Kingdom.
Age – The occurrence is of Berriasian-Valanginian age.
Diagnosis – neural arch proportionally very tall with zygapophyses higher above centrum that cotyle height; neural arch slopes forward approx. 22 degrees relative to horizontal axis of centrum; broad, flat area of featureless bone on lateral face of neural arch; asymmetric neural canal, small and circular in posterior aspect but tall and teardrop-shaped in anterior aspect; supporting laminae form vaulted arch within anterior neural cavity; anteroposterior length of neural arch 80% centrum length.
BMNH R2095 is a partial dorsal vertebra catalogued as “Morosaurus brevis”. Most of the centrum and the neural arch are preserved, but the condyle is broken, and the upper part of the neural arch and entire spine are missing, as well as all the processes – pre- and postzygapophyses, diapophyses and parapophyses. However, sufficient laminae remain to allow the positions of the processes to be inferred with some certainty.
The most striking feature of this specimen is the extreme height and forward-swept orientation of the neural arch, which appears to be a genuine osteological feature and not the result of post-mortem distortion. Although the vertebra is broken off below the diapophyses, its measurable height (approx. 300mm measured perpendicular to the axis of the centrum) greatly exceeds the centrum length (approx. 190mm measured at the top of the centrum; the anteroventral portion of the centrum is missing but a maximum length of about 200mm is indicated). The base of the neural spine is about 180mm in anterodorsal length, 90% of the estimated full length of the centrum. The preserved part of the neural arch extends 170mm above the dorsal margin of the anterior part of the centrum.
The cotyle is only mildly concave, but sufficiently so to establish the orientation of the vertebra, which is otherwise obscure due to the absence of zygapophyses. The cotyle is approx. 160mm high and 170mm wide. A clean break of the condyle preserves the dorsal part of a median septum and a pair of ventromedially directed lateral septa, indicative of an extensively pneumatised centrum. The ventral portion of the broken condyle is obscured by a catalogue note. The centrum has a very mild ventral keel, and its ventral border in lateral view is somewhat dorsally arched.
The pleurocoels are positioned dorsally on the centrum, and about midway between the anterior and posterior margins of the neural arch into which they intrude. They are roughly oval in shape, their height being approx. 60% of their length, with a slightly sharper corner at the posterior end than at the anterior. They are medium sized, being approx. half as long as the centrum.
The neural arch is better preserved on the left side, and this side will the primary focus of the following description. So far as can be ascertained, the right side matches it except where explicitly stated below.
Above the pleurocoel on the left side is a very sharp-lipped lateral ridge, running anterodorsally for about 90mm; this is absent on the right side, seemingly not due to damage but to intravertebral variation. From a point anterior to the end of this ridge, a vertically oriented ACPL runs up about 70mm to a cross-shaped junction of laminae near the anterior portion of the arch, which we interpret as the site of the parapophysis. From here, part of an anteriorly directed PRPL is preserved, along with the ventral portion of a posterodorsally directed lamina which is perhaps best interpreted as a PPDL, and a posteroventrally directed accessory lamina connecting the parapophysis to the portion of the neural arch about 90mm above the pleurocoel. This cannot be interpreted as a PCPL, as it does not approach the centrum, and indeed extends only about 30mm. Where it merges with the arch, another accessory lamina arises, directed posterodorsally, presumably to the postzygapophysis. The PPDL, accessory parapophyseal and accessory postzygapophyseal lamina form three sides of a diamond-shaped fossa; the fourth side, presumably formed by a PODL, is not preserved. The near-vertical orientation of the PPDL indicates that the diapophysis was located some distance dorsal to the parapophysis, further extending the inferred height of the neural arch.
The location of the parapophysis high on the neural arch indicates that this is a posterior dorsal vertebra.
Between the sharp anterodorsally oriented ridge and the laminae described above, the lateral face of the neural arch is flat and featureless, a feature not observed in any other sauropod vertebra.
In posterior view, the pedicels of the neural arch are robust pillars, leaning slightly inwards, measuring about 30mm in width and extending at least 120mm upwards before damage obscures their further extent. They enclose a neural canal that is almost exactly circular, measuring 40mm in each direction. There is no trace whatsoever of the postzygapophyses or hyposphene and no indication that the latter was attached to the preserved portion of the arch. It must be assumed, then, that these features were located on the lost, more dorsal, part of the neural arch. It is safe to assume that the hyposphene, if present, was located at least 160mm above the centrum (measured from the floor of the neural canal) and the postzygapophyses at least 200mm; a yet higher location is by no means precluded.
In anterior view, the pedicels are also robust, about 20mm in width, extending at least 100mm to the point where they are broken. Here, however, the neural canal has no roof, instead forming a large teardrop-shaped vacuity 120mm in height and 55mm in width. The dorsal portion of this vacuity is bounded by a pair of gently curved dorsomedially directed laminae, which meet at a 55-degree angle to form an arch above the neural canal. The vacuity is filled with matrix, so the extent of its penetration into the neural arch cannot be assessed. The prezygapophyses are entirely absent; their articular surfaces cannot have been less than 160mm above the floor of the neural canal.
The uppermost preserved portion of the vertebra is a flat, anterodorsally directed “apron”, about 15mm thick and 120mm wide. If this is real bone, it may be interpreted as conjoined prezygapophyseal laminae, being composed of both CPRLs and PRPLs. This interpretation would preclude an intraprezygapophyseal hypantrum, in which case no hyposphene would have been present. However, this may be simply be unremoved matrix; further preparation will resolve the point.
Comparison and Interpretation
The concave curvature of the cotyle indicates that R2095 is a sauropod vertebra (Salgado et al. (1997 p. 6), Wilson and Sereno (1998 p. 42-43)); the height of the neural arch exceeding that of the centrum places it within the clade (Barapasaurus + Eusauropoda) (Upchurch (1998 p. B6)); [### I don't understand Upchurch 1998's character B7=101 – apparently it's described in Bonaparte (1986)]; and the deep pleurocoel places it within or close to Neosauropoda (Salgado et al. (1997 p. 8-9); Wilson and Sereno (1998 p. 44); Upchurch (1998 p. B5)). Possession of an ACPL suggests placement with Neosauropoda (Upchurch (1998 p. H3)), a group of advanced sauropods consisting of diplodocoids, camarasaurs, brachiosaurs and titanosaurs, and in some phylogenies Haplocanthosaurus.
ACPLs are convergently acquired in euhelopodids (Upchurch (1998 p. D4)), suggesting an alternative identity for R2095. The euhelopodid Mamenchisaurus hochuanensis indeed has tall neural arches in its posterior dorsals; however, it lacks pleurocoels and its centra are amphiplatyan (Young and Zhao (1972 p. fig. 7)), ruling out a euhelopodid interpretation.
Tall neural arches are not unusual in the dorsals of diplodocoids; and while strongly forward-sloping neural arches are not known in this group, a mild anterodorsal inclination of the neural spine is sometimes found. Taken alone, then, these gross morphological characters of the neural arch suggest that R2095 may represent a diplodocoid. However, the length of the centrum, especially for a posterior dorsal, argues against this interpretation: the posterior dorsals of diplodocoids typically have centra approximately 60% the length of their cotyle height, compared with 140% for R2095. Furthermore, the base of the neural spine of R2095 is much longer anteroposteriorly than in diplodocoids, and the pleurocoels of diplodocoids are smaller, located more anteriorly on the centrum, and less pronouncedly oval.
Instead, the concave cotyle in so posterior a dorsal suggests a macronarian identity (Salgado et al. (1997 p. 9)). The concavity is sufficiently deep to rule out the possibility of the vertebra being amphicoelous, i.e. it must have had a convex condyle; this is also interpreted as a macronarian synapomorphy (Upchurch (1998 p. J6)). Among macronarians, the dorsally arched ventral margin of the centrum in lateral view suggests either a brachiosaurid or camarasaurid identity rather than titanosaurian (Wilson and Sereno (1998 p. 51)). Further, the neural spines of titanosaurs are posteriorly inclined by as much as 45 degrees. Although the neural spine of R2095 is not preserved, the 20 degree anterior slope of the neural arch makes such a posterior slope of the spine very unlikely. This suggests that the vertebra is camarasaurid or brachiosaurid.
The posterior dorsals of camarasaurs, such as that figured in Ostrom and McIntosh (1966), can have somewhat dorsoventrally elongated neural spines. However, the medium and anteroposteriorly elongate pleurocoel of R2095 is not a good match for that specimen's large, round pleurocoel (### check against other camarasaur dorsals), and the neural arches of camarasaur dorsals either are vertical or slope backwards rather than forwards. R2095's anteriorly large neural canal is also not found in camarasaurs (### at least not the ones I have photos of).
Instead, the length of the centrum relative to the cotyle height, with an EI (sensu Wedel et al. (2000)) of approx. 1.4, suggests titanosauriform identity (Upchurch (1998 p. K3)). This placement is corroborated by the shape of the pleurocoel, with a more acute posterior margin than anterior (Upchurch (1998 p. M1)), and the anteroposteriorly elongate oval shape of the pleurocoel (Salgado et al. (1997 p. 18-19)). Conversely, however, the shallowness of the cotyle curvature argues against its being a titanosauriform, since in brachiosaurs, camarasaurs and titanosaurs, even the posterior dorsals are strongly opisthocoelous (Wilson and Sereno (1998 p. 43), 51).
The long centrum particularly suggests a brachiosaurid, as these have the proportionally longest posterior dorsal centra of all sauropods. Since brachiosaurs are overwhelmingly the most common sauropods in the Wealden Formation, this identity is also likely on palaeobiogeographical grounds. In anterior view, the neural canal of R2095 is somewhat reminiscent of that of the Brachiosaurus brancai referred specimen HMN AR1, which has an extremely large (and fully prepared) neural canal. However, the pedicels of that specimen are much less robust than those of R2095, and its neural canal in posterior view is also large, unlike the small, circular opening of R2095. Furthermore, the neural arch of AR1 does not slope forwards; nor does that of any other known brachiosaur. Neither is the somewhat posteriorly positioned pleurocoel of R2095 typical of non-English brachiosaurs, although it is found in the holotype of “Ornithopsis” and in the “Eucamerotus” paratype specimens (sensu Blows (1995)).
If the identification of the “apron” as conjoined prezygapophyseal laminae is correct, and the vertebra therefore lacked a hyposphene, this would greatly constrain its identity. Hyposphenes are primitive for sauropods, and are lost only in Titanosauridae, indicating a titanosaurid identity (Salgado et al. (1997 p. 20); Upchurch (1998 p. Q2)). However, what remains of the neural arch does not have the “inflated” appearance characteristic of titanosaurs: the laminae are gracile and clearly delineated, whereas those of titanosaurs tend to be more robust and to merge into the wall of the neural arch: for example, the gracile, vertical ACPL of this specimen does not resemble the more robust and diagonally oriented centroparapophyseal lamina of titanosaurs (Salgado et al. (1997 p. 19) and fig. 2). R2095 also lacks the thick, ventrally forked infradiapophyseal laminae considered synapomorphic for titanosaurs (Salgado et al. (1997 p. 19)) and its pleurocoel is not located anteriorly within an elongate ovoid depression (Bonaparte and Coria. (1993 p. 272) ### I've not seen this paper myself).
### Could it be close to Haplocanthosaurus? According to Wilson and Sereno (1998 p. 19), Haplocanthosaurus dorsal neural arches lack ACDLs (which is hard to assess for R2095), have elongate CPOLs (could be true here) and have diapophyses that project 45 degrees upwards (which seems at least compatible with what is preserved in R2095). Clearly I need to look at the plates in Hatcher (1903).
The balance of evidence favours the interpretation that R2095 is a highly derived brachiosaurid, based on the following characters: concave cotyle (and by implication, convex condyle) in a posterior dorsal; centrum 1.4 times as long as tall; base of neural spine 90% as long as centrum; medium-large pleurocoels; pleurocoels oval in shape, 60% as tall as they are long; posterior margin of pleurocoels more acute than anterior margin; dorsally arched ventral border of centrum; neural spine inferred not to be posteriorly inclined as in titanosaurs; laminae gracile rather than robust as in titanosaurs; infradiapophyseal lamina not ventrally forked.
Against these characters, the shallowness of the cotyle argues against a brachiosaurid identification. If the hyposphene/hypantrum articulation was absent, this would also count against a brachiosaurid identity, but further preparation is required to determine this. In any case, these non-brachiosaur characters are easily outweighed by the brachiosaur characters enumerated above.
Within Brachiosauridae, R2095 is unique in the possession of a very tall neural arch, in the forward slope of the neural arch, and in the broad, flat area of featureless bone on the lateral face of the neural arch.
Lydekker (1892)) reported that BMNH R2095 was discovered in Wealden rocks of Hastings, but beyond that nothing is recorded of locality or stratigraphic data. It is assumed that the specimen was discovered at or around Fairlight, the location where Rufford discovered the majority of his Wealden fossils. Hastings Beds Group exposures at and around Fairlight are of both the Ashdown Beds Formation and the Wadhurst Clay, and consequently it remains unknowable which of these units yielded the specimen.
[### will expand when I get more info on where Rufford collected from – stuff to check]
While the specimen described here represents a diagnosable macronarian taxon, the possibility that it is referable to one of the named Hastings Beds Group sauropod taxa has to be considered. Two named sauropod taxa are known from the Hastings Beds Group, one of which has two binomials and a complex nomenclatural history. Four proximal caudal vertebrae (BMNH R2544-2547) and three chevrons (BMNH R2548-2550) from the Hastings Beds Group of Cuckfield, together with other specimens from Sandown Bay on the Isle of Wight, were named Cetiosaurus brevis Owen, 1842. This is the first named Cetiosaurus species that is not a nomen dubium (and thus technically the type species) but, because the name Cetiosaurus is historically most associated with the Middle Jurassic Oxfordshire species C. oxoniensis, the most sensible course of action is to petition the ICZN to make this the type species, as is planned (Upchurch and Martin (2002, 2003)). Cetiosaurus brevis is clearly not congeneric with C. oxoniensis: accordingly, the former is referred to as “C.” brevis from here on. The Isle of Wight “C.” brevis material was demonstrated to be iguanodontian in nature by [Melville1849] who went on to provide the new name “C.” conybeari Melville 1849 for the Cuckfield sauropod component of “C.” brevis. As has been widely recognized (### refs for those who recognized this – Ostrom 1970 etc.), Melville’s (1849) course of action was inadmissible as “C.” brevis was still available for this material (Steel (1970), Upchurch and Martin (2003)) and, accordingly, “C.” conybeari is a junior objective synonym of “C.” brevis.
Discovered adjacent to the Cuckfield “C.” brevis vertebrae and chevrons was a large humerus. [Mantell1850] referred this to “C.” brevis under Melville’s (1849) name “C.” conybeari, but decided that the taxon was distinct enough for its own genus, Pelorosaurus Mantell 1850. (As shown by Cadbury (2001), Mantell considered the name Colossosaurus [### in quotes? Italics?] for this humerus). Though still discussed apart in most taxonomic reviews (Naish and Martill (2001), Upchurch and Martin (2003)), it is therefore clear that Pelorosaurus conybeari and “C.” brevisare objective synonyms, with the latter having priority. The identity and validity of this material remains problematic. The humerus lacks autapomorphies and, though brachiosaurid-like and hence conventionally identified as representing a member of that group (indeed, McIntosh (1990) even suggested that Brachiosaurus and Pelorosaurus might be synonymous on the basis of this similarity [### check]), it differs in having a less prominent deltopectoral crest. Furthermore the “C.” brevis caudal vertebrae are titanosaur-like in at least one feature (the absence of a hyposphenal ridge). On the basis of these observations, Upchurch et al. (2004) proposed that this material be allocated to Titanosauriformes incertae sedis. It is therefore conceivable that BMNH R2095 is referable to “C.” brevis, though this is not demonstrable given the lack of dorsal vertebrae in the holotype.
Lydekker (1890, 1893) and Swinton (1936) referred to “C.” brevis as Morosaurus brevis. [### More on this to come … ]
The second named Hastings Beds Group sauropod is Pelorosaurus becklesii Mantell 1852, based on a partial humerus, ulna and radius with associated skin, discovered at Hastings. On the basis of the robustness of its limb bones, this taxon appears to be a significantly early titanosaur (Upchurch (1995), Upchurch et al. (2004)) and it should not be considered congeneric with Pelorosaurus conybeari. Because the identification of “P.” becklesii as a titanosaur is secure, BMNH R2095 cannot be referred to it.
A large sauropod metacarpal from Bexhill has been identified as diplodocoid ([Anon2005]). If correctly identified, this specimen indicates the presence of at least three sauropod taxa in the Hastings Beds Group (diplodocoids, basal titanosauriforms and titanosaurs). The presence of these several different taxa in coeval or near-coeval sediments is not unexpected given the high generic-level sauropod diversity present in many other sauropod-bearing units.
The asymmetric neural canal, small and circular in posterior view but large and vaulted in anterior view, is also seen in several “Ornithopsis” and “Eucamerotus” vertebrae, and may be characteristic of a British brachiosaur radiation.
### Is it also the case that British brachiosaurs tend to have more anteriorly positioned pleurocoels than American and African specimens?
### to follow
### to follow
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